The present invention relates generally to methods of operating diesel engines and to diesel engine arrangements and, more particularly, to such methods and diesel engine arrangements that involve plural operating modes.
Diesel engines are often operated in a plurality of discrete operating modes that differ from one another with respect to one or more different setpoints of base engine actuators. For example, in one mode of operation, an engine arrangement including an EGR line might have a setpoint in which an EGR valve is open while, in another mode of operation, the EGR valve may be closed.
Some engines are controlled to have a variety of different base actuators set in particular way for different operating modes. For example, one setting of base actuators may produce a “fuel economy mode” in which the object is to conserve fuel, regardless of, for example, NOX levels output from the engine arrangement. Another setting of base actuators may produce a “low heat mode” in which the object is to produce engine temperatures or exhaust at a particular temperature. Yet another setting of base actuators may produce a “high heat mode” in which the object is to produce higher engine or exhaust temperatures than are produced at low heat mode, such as for purposes of active regeneration of a diesel particulate filter (DPF).
Air quality regulations in many countries presently limit various emissions such as oxides of Nitrogen (NOX) from, e.g., vehicles. Various exhaust aftertreatment systems and components have been developed to comply with these requirements. In efforts to comply with these requirements, the focus is typically on whether, under given operating conditions, the emissions limits are met. The inventors have recognized that there has been substantially no consideration of the relative fuel economy of operation with one set of base actuator control setpoints that complies with emissions requirements versus operation with another set of base actuator control setpoints that also complies with the emissions requirements. They have recognized that there may be circumstances where it may be desirable to switch to another operating mode from a current operating mode, even though operation in the current mode complies with the emissions requirements, in order to achieve better fuel economy.
According to an aspect of the present invention, a method is provided of operating a diesel engine having an exhaust aftertreatment system (EATS) including one or more apparatus for controlling exhaust NOX levels, the engine comprising a plurality of systems and components, at least some of which systems and components being adapted to be set to one or more control setpoints for one or more base actuators of the engine. The method comprises establishing a plurality of engine operating modes, each operating mode differing from any other operating mode with respect to at least one control setpoint, for each operating mode, mapping fuel economy versus NOX levels exiting the EATS, selecting an operating mode from among the plurality of operating modes so that exhaust exiting the EATS contains NOX at no more than a predetermined NOX level and a least amount of fuel is consumed per unit energy; and operating the engine in the selected operating mode.
According to another aspect of the present invention, a method is provided of operating a diesel engine having an exhaust aftertreatment system (EATS) including one or more apparatus for controlling exhaust NOX levels. The method comprises operating the engine in a first mode with a first series of control setpoints for a plurality of base actuators of the engine, operating the engine in a second mode with a second series of control setpoints for the plurality of base actuators, at least one control setpoint of the first and second series of control setpoints being different, tracking exhaust mass or volume flow through the EATS, NOX levels exiting the EATS, and temperature in the EATS for the engine over a plurality of engine speeds and loads in the first mode and in the second mode, and selecting one of the first mode and the second mode so that, for a given engine speed and load, exhaust exiting the EATS contains NOX at no more than a predetermined NOX level and a least amount of fuel is consumed per unit energy.
According to another aspect of the present invention, a diesel engine arrangement comprises a diesel engine having an exhaust aftertreatment system (EATS), a NOX sensor arranged to sense NOX levels exiting the EATS, and a controller arranged to receive a signal from the NOX sensor, the controller comprising a map of fuel economy versus NOX levels exiting the EATS for a plurality of engine operating modes, each engine operating mode differing from any other engine operating mode with respect to at least one base actuator of the engine, the controller being programmed to select one of the plurality of operating modes and cause the engine to operate in the selected operating mode so that, for a given engine speed and load, exhaust exiting the EATS contains NOX at no more than a predetermined NOX level and a least amount of fuel is consumed per unit energy.